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2	Disclosures NONE
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4	Introduction Sudden onset sensorineural hearing loss (SHL), defined as 30 dB or more sensorineural hearing loss over a minimum of three contiguous audiometric frequencies occurring within 3 days or less, is considered a medical emergency. Worldwide, around 15,000 cases are reported annually, with about 4,000 of those arising in the United States. The highest incidence of SHL occurs between the ages of 50 and 60 years, with almost equal incidence between men and women, and 98% of cases are unilateral in nature.
5	Etiology The majority of SHL cases are idiopathic, eluding diagnosis despite extensive evaluation, with etiology apparent in only 10% of cases. Potential SHL etiology includes: Viral and Infectious: Herpesvirus, Meningococcal Meningitis with Labyrinthitis Ossificans, Human Immunodeficiency Virus, Lyme Disease, Syphilis Autoimmune: Systemic Lupus Erythematosus, Relapsing Polychondritis, Polyarteritis Nodosa, Sarcoidosis Traumatic: Hemorrhagic Labyrinthitis, Perilymph Fistula, Temporal Bone Fracture, Inner Ear Concussion, Stapedectomy, Toxins Vascular: Dolichoectasia of Vertebrobasilar Artery, Vascular Disease of Microcirculation, Sickle Cell Disease, Cardiopulmonary Bypass Neurologic: Multiple Sclerosis, Focal Pontine Ischemia, Migraine Neoplastic: Acoustic Neuroma, Metastasis to Inner Auditory Canal, Endolymphatic Sac Tumor, Leukemia
6	Anatomy
7	Lesions Causing Sensorineural Hearing Loss Sensory Causes: Cochlear Lesions Neural Causes: Retrocochlear Lesions
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12	Inner Ear Inflammatory Lesions Bacterial Labyrinthitis Labyrinthitis Ossificans Others Hemorrhagic Labyrinthitis
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14	Labyrinthitis Ossificans
15	Hemorrhagic Labyrinthitis
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22	Superficial Siderosis
23	Ramsey Hunt Syndrome abnormal enhancement of left CN VII in this patient with herpetic infection
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32	Endolymphatic Sac (Adenomatous) Tumor
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35	Vascular Lesions Aberrant Internal Carotid Artery Dehiscent Jugular Bulb Vascular Loops Aneurysm Tortuous and Ectatic Vessels Persistent Stapedial Artery Glomus tympanicum / Glomus jugulare
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40	Vertebrobasilar Dolicoectasia
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44	Otodystrophies of the Temporal Bone Genetic Otosclerosis (otospongiosis) Fenestral type (conductive hearing loss) Cochlear type (sensorineural hearing loss) Osteogenesis Imperfecta Imperfecta tarda
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49	Fibro-osseous Lesions of the Temporal Bone Paget’s Disease Progressive monostotic and polystotic Fibrous Dysplasia Progressive inherited monostotic and polystotic
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56	Approach and Treatment: Urgent evaluation is necessary to rule out treatable causes of SHL, including autoimmune, traumatic, and neoplastic etiologies. For all patients, an audiogram should be performed, while those with asymmetric hearing loss should additionally have magnetic resonance imaging (MRI). For autoimmune forms, steroids are the cornerstone of treatment, while for traumatic forms, strict bed rest, avoidance of straining, and possibly surgery may be considered. For idiopathic SHL, the most appropriate therapy is controversial and may include anti-inflammatory/immunologic agents, diuretics, antiviral agents, vasodilators, volume expanders, defibrinogenators, and calcium antagonists. In one study, treatment with steroids resulted in an 89% recovery rate compared to 44% recovery in those untreated.
57	Conclusion: Sudden onset sensorineural hearing loss may be devastating to patients and challenging for clinicians to diagnose and treat. Although the etiology usually remains undiagnosed, all patients should undergo audiometry with MR imaging for those with asymmetric hearing loss. Modern fast high-resolution CT is often the preferred imaging modality in children often avoiding sedation while MRI with contrast is the preferred imaging modality for adults. Treatment continues to be controversial. For those with moderate to severe hearing loss, steroids have been shown to significantly improve recovery of hearing and are favored for treating autoimmune and idiopathic forms.
58	References: Cole, R. R., Jahrsdoerfer, R. A.: Sudden hearing loss: an update. The American Journal of Otology 1988; 9:211-215 (May). Fetterman, B. L., Saunders, J. E., Luxford, W. M.: Prognosis and Treatment of Sudden Sensorineural Hearing Loss. American Journal of Otology 1996; 17:529-36. Gulya, A. J.: Sudden sensorineural hearing loss: an otologic emergency. Comprehensive Therapy 1996; 22(4):217-221. Muller C, Vrabec J, Quinn FB: Sudden sensorineural hearing loss. Grand Rounds Presentation, UTMB, Department of Otolaryngology, 2001, June 13. Park, S. U. et al.: The usefulness of MR imaging of the temporal bone in the evaluation of patients with facial and audiovestibular dysfunction. Korean Journal of Radiology; 2002 March; 3(1):16-23. Schuknecht, H. F., Donovan, E. D.: The pathology of idiopathic sudden sensorineural hearing loss. Achives of Otolaryngology 1986; 243:1-15. Sudden onset sensorineural hearing loss Vasama, J., Linthicum, F. H.: Idiopathic sudden sensorineural hearing loss: Temporal bone histopathology study. Ann Otol Rhinol Laryngol 2000; 109:527-532.